Catalytic oxidation of propylene and isobutylene to aldehydes and acids



United States Patent 3,493,608 CATALYTIC OXIDATION OF PROPYLENE ANDISOBUTYLENE T0 ALDEHYDES AND ACIDS Jamal S. Eden, Akron, Ohio, assignorto The B. F. Goodrich Company, New York, N.Y., a corporation of New YorkNo Drawing. Filed Jan. 21, 1966, Ser. No. 522,032

Int. Cl. C07c 51/32 US. Cl. 260-533 Claims ABSTRACT OF THE DISCLOSUREPropylene and isobutylene are oxidized to the equivalent unsaturatedaldehydes and carboxylic acids at an elevated temperature in thepresence of a catalyst containing molybdenum oxide, tellurium oxide anda copper phosphate.

This invention relates to new and useful catalysts and to a method ofpreparing unsaturated aldehydes and unsaturated carboxylic acids byoxidation of unsaturated hydrocarbons at an elevated temperature, andrelates more particularly to catalysts comprising a mixture of amolybdenum oxide, tellurium oxide and a copper phosphate in a molarratio of 100 M00 100 TeO and 10-100 of a copper phosphate and to amethod of preparing acrolein and acrylic acid, or methacrolein andmethacrylic acid by passing vapors of propylene or isobutylene and anoxygen-containing gas over the catalyst at a temperature of from about325 C. to about 550 C. The catalyst can also be designated as MO1 Te1 1Cu2 2oP2 2 O 12o the P preferably being in the form of a phosphate,i.e., each P is attached to 3 or 4 oxygen atoms.

Numerous attempts have been made in the past to prepare products ofhigher oxidation state from hydrocarbons, especially from the normallygaseous hydrocarbons. However, prior catalysts and procedures foroxidizing monoolefinic gaseous hydrocarbons to monoolefinicallyunsaturated aldehydes or monoolefinically unsaturated carboxylic acidswith the same number of carbon atoms as the hydrocarbon havingshort-comings. The catalysts either have a very short active life, orthey convert only a portion of the hydrocarbon to desired end groups perpass; they oxidize the hydrocarbon excessively to form high proportionsof carbon monoxide or carbon dioxide or both; they are not sufiicientlyselective, so that the hydrocarbon molecule is attacked at both theolefinic unsaturation and at a methyl group; or the oxidation of theolefin does not proceed beyond the aldehyde stage.

It is therefore unexpected to find a catalyst having unusually long lifethat will convert a substantially amount, more than 50% per pass, of agaseous monoolefin such as propylene or isobutylene to yield very highproportions of acrolein and acrylic acid, or methacrolein andmethacrylic acid. It is also unexpected to find a catalyst that producesa wide ratio of olefinic aldehyde to monoolefinically unsaturatedcarboxylic acid by controllable changes in reaction conditions orcatalyst composition at good mol percent efiiciencies for the aldehydeand unsaturated carboxylic acid. Usually when the efliciency forconversion of the hydrocarbon to aldehyde is high the efficiency for theconversion to acid is low and vice versa. This provides a degree offlexibility in the process, so as to provide means for obtaining aproduct mix that is needed at any particular time during commercialoperation.

THE REACTANTS The essential reactants are (1) propylene or isobutyleneand (2) an oxygen-containing gas, which can be pure oxygen, oxygendiluted with an inert gas, oxygen enriched air or air without additionaloxygen. For reasons of economy, air is the preferred oxygen-containingreactant.

For the purpose of this invention the hydrocarbons which are oxidizedcan be defined generically by the formula CH =CH2 wherein it is alsoapparent that the end products formed result from the oxidation of onlyone methyl group on the hydrocarbon molecule While the terminal CH Cremains intact.

'Stoichiometric ratios of oxygen to olefin for the purpose of thisinvention are 1.5 to 1. Slightly lower amounts of oxygen can be used ata sacrifice of yield. It is preferred, however, to use 33 to 66% excessoxygen. Larger excesses do not impair the yields of aldehydes and acids,but for practical considerations an excess much above would requireextremely large equipment for a given production capacity.

The additiOn of steam into the reactor along with the hydrocarbon andoxygen-containing gas is desirable but not absolutely essential. Thefunction of steam is not clear, but it seems to reduce the amount ofcarbon monoxide and dioxide in the efiluent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbonssuch as propane are rather inert under the reaction conditions.Nitrogen, argon, krypton or other known inert gases can be used asdiluents if desired but are not preferred because of the added cost.

THE CATALYST AND ITS PREPARATION There are several methods for thepreparation of the catalyst, which can be supported or unsupported. Itis possible to dissolve each of the starting ingredients in water andcombine them from the aqueous solutions or the ingredients can be dryblended. Because of the more uniform blend obtained by the solutionprocedure, it is preferred.

The general procedure for preparing a catalyst from water-solubleingredients is to dissolve the requisite amount of a molybdenum salt, atellurium salt and a copper salt in water. Add the requisite amount ofphosphoric acid to the copper salt solution. Add the tellurium saltsolution to the molybdenum salt solution and then add the coppersalt-phosphoric acid mixture to the molybdenum-tellurium salt mixture.The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding a dry support or anaqueous slurry thereof to the aqueous solu tion of catalyst or theaqueous catalyst ingredients can be added to the slurry of the support.

Alternatively a slurry of the catalyst ingredients can be prepared inwater, then dried and baked. For supported catalysts the aqueous slurryof the catalyst ingredients can be added to an aqueous suspension of thesupport or vice versa, and then dried and baked.

Another method is to blend the dry ingredients of the desired particlesize and then mix them thoroughly. Thorough blending and uniformparticle size is desired.

A specific example of the solution method is now set forth.

(1) Dissolve 52.98 g. of ammonium molybdate in 100 ml. of Water and addto 100 g. of an aqueous colloidal dispersion of microspheroidal silicain a concentration of 30-35% SiO (Ludox H.S.).

(2) 15.96 g. of TeO dissolved in 40 ml. of concentrated HCl is added to(1).

(3) Dissolve 34.1 g. of CuCl -2H O in 50 ml. of water and add 23.1 g. of85% H PO Add this mixture slowly to the mixture of (l) and (2).

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, thecatalyst is ground to the desired mesh size and sieved.

Among the suitable supports are silica, silica-containing materials,such as diatomaceous earth, kieselguhr, silicon carbide, clay, aluminumoxides and even carbon, although the latter tends to be consumed duringthe reaction.

The exact chemical structure of the catalysts made by the aboveprocedures is not known, but catalysts with molar ratios of 100 Mo,10100 Te and 10100 of a copper phosphate can be used for oxidizing themonoolefinic hydrocarbon to aldehyde and/or carboxylic acid. Thecatalyst contains chemically bound oxygen so that the generic formulacan be written as M TeO Cu P O or other copper phosphate 10-100. Thephosphate can be a PO; radical, a pyrophosphate, or a polyphosphate.

REACTION CONDITIONS The reaction can be carried out in either a fixed orfluidized catalyst bed.

The reaction temperature can range from about 300 to 450 C. for theoxidation of propylene but the preferred range is from about 350 toabout 425 C. Below 350 C. the conversion per pass is lower and lowtemperature tends to produce more aldehyde than desired. Usually, alonger contact time is needed at lower temperatures to obtain the yieldsof desired products obtainable at higher temperatures. Above 425 C. inthe propylene oxidation some of the desired end products appear to beoxidized to carbon oxides. This is much more apparent at 450 C. Forisobutylene, oxidation temperatures of 375550 are desirable with thepreferred range being 300-450 C.

The molar ratio of oxygen to propylene or isobutylene should be at least2 to 1 for good conversion and yields. Some excess oxygen, 33 to 66 molpercent is even more desirable and is preferred. There is no criticalupper limit as to the amount of oxygen, but when air is used as theoxygen-containing gas it becomes apparent that too great an excess willrequire large reactors, pumping, compressing and other auxiliaryequipment for any given amount of desired end product. It is thereforebest to limit the amount of air to provide a 33 to 66% excess of oxygen.This range provides the largest proportion of acid, under given reactionconditions. Also, since care is needed to avoid an explosive mixture,the limiting of air aids in that direction.

The molar ratio of steam to propylene or isobutylene can range from 0 toabout 5 to 7, but best results are obtained with molar ratios of about 3to 5 per mol of olefin and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to 70seconds. Best results are obtained in a range of about 8 to 54 secondsand this range is preferred. Longer contact times usually favor theproduction of acid at any given temperature.

The particle size of catalyst for fixed bed operations used is from 1018mesh. As is known, for fixed beds, the size may be of a wider rangeparticle size. For fluid bed systems the catalyst size should be from80325 mesh (U.S. Sieve).

The reaction can be run at atmospheric pressure, in a partial vacuum orunder induced pressure up to 50l00 4- p.s.i. Atmospheric pressure ispreferred for fixed bed systems and a pressure of 1 to 100 p.s.i. forfluid bed reactions. Operation at a pressure which is below the dewpoint of the unsaturated acid at the reaction temperature isadvantageous.

The data in the examples show that wide variations in percentages ofunsaturated acids and aldehydes can be obtained with a single catalyst,using fixed ratio of reactants but changing the temperature and/ orcontact time. Further variation is obtainable by controlling the othervariables in the reaction including the catalyst compositions within thelimits set forth herein.

The examples are intended to illustrate the invention but not to limitit.

THE EXAMPLES A series of runs was made in a fixed bed reactor of a highsilica (Vycor) glass tube 12 inches long and 30 mm. outer diameter. Thereactor had three inlets, one for air, one for steam and one forpropylene. Three external electrically operated heating coils were woundon the reactor. One of the coils extended along the entire length of thereactor and each of the remaining coils extended only about one half thelength of the reactor.

Outlet vapors were passed through a short water cooled condenser.Uncondensed gases were passed through a gas chromatograph (Perkin-ElmerModel 154D) and analyzed continuously. The liquid condensate was weighedand then analyzed for acrylic acid and acrolein in the gaschromatograph.

The reactor was filled with ml. of a catalyst made by the solutionmethod described above, using a ratio of 75 M00 15 TeO and 25 Cu P OEmpirically the catalyst IS M0 Tc Cu P O and thfi P IS present as P OThe catalyst had a mesh size of 10-18 (U.S. Sieve).

Steam at a temperature of 20025 0 C. was first passed into the reactor.Then propylene and air were separately fed into the stream of watervapor. This mixture then passed through a pre-heater and entered thereactor at about 200250 C. The reactor was pre-heated to about 285 C.before the gas feed was begun.

The ratio of reactants was about 2.52 mols of oxygen and 3.88 mols ofsteam per mol of propylene. Cold contact time was 18.5 seconds. Thetable below summarizes the data obtained in these runs:

Mol Percent Yield on Mol Percent Propylene Converted 1. A method forpreparing monoolefinic aldehydes and monocarboxylic acids by theoxidation of a monoolefin selected from the group consisting ofpropylene and isobutylene comprising contacting said monoolefin andoxygen in a motor ratio of 1 mol of said monoolefin and about 1.5 to 4mols of oxygen at a temperature of from about 325 C. to 550 C. with acatalyst consisting essentially, on a molar basis, of 100 molybdenumoxide, 10- 100 tellurium oxide and 10-100 of a copper phosphate.

2. The method of claim 1 wherein a mixture of acrolein and acrylic acidis prepared from propylene in the presence of up to 7 mols of watervapor per mol of propylene at a temperature from about 350 C. to about450 C., the molar ratio of oxygen to propylene is at least 2 to 1, andthe copper phosphate is copper pyrophosphate.

3. The method of claim 2 wherein the oxygen is supplied in air and themolar ratio of catalyst constituents is about 75 M00 15 TO2 and 25CUZPZOI'I.

5 6 4. The method of claim 1 wherein a mixture of meth- References Citedacrolein and methacrylic acid is prepared from isobutyl- UNITED STATESPATENTS ene in the presence of up to 7 mols of Water vapor per mol ofisobutylene, at a temperature from about 375 C. 311921259 6/1965Fetterly et a1 260533 to 550 C., the molar ratio of oxygen toisobutylene is at least 2 to 1, and the copper phosphate is copper pyrodLORRAINE WEINBERGER Pnmary Exammer phosphate. D. STENZEL, AssistantExaminer 5. The method of claim 4 wherein the oxygen is supplied in airand the molar ratio of catalyst constituents is about 75 M00 15 TeO and25 Cu P O 10 252-437; 260-604 @3 3? UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION -.Pa x;ent No. 3, 93, Dated February 3, 97

Inventorksb Jamal S. Eden It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 4, line 62, Claim 1, "motor" should read --mola.r--.

SIGNED KND SEALED JUL 1 4870 Amt:

B when mun 1:. sum, m. ofzim Oomissioner of Patents

